Four-stroke Otto engine having hybrid control

ABSTRACT

A four-stroke Otto engine. At least two intake valves of the engine have an open position and a closed position, and include a main intake valve and an additional intake valve. A camshaft moves the main intake valve into its open position and into its closed position, and a transmission element transmits a motion of the camshaft to the main intake valve. The transmission element includes a cutoff apparatus actuatable independently of the camshaft for cutting off a transmission of the actuation of the camshaft to the main intake valve for keeping the main intake valve in its closed position in a lower partial load and rpm range of the engine. An operating apparatus connected to the additional intake valve actuates the additional intake valve independently of the actuation of the main intake valve for moving the additional intake valve into its open position in a lower partial load and rpm range of the engine and into its closed position in an upper partial load and rpm range of the engine. The operating apparatus further adjusts at least one of a valve stroke of the additional intake valve, a valve opening time of the additional intake valve and a valve closing time of the additional intake valve as a function of engine load. An intake control device controls the cutoff apparatus and the operating apparatus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a four-stroke Otto engine having at least onecylinder and, for each cylinder, at least one intake valve with positivecontrol and at least one outlet valve with positive control, with atleast one intake conduit for the supply of air or an air-fuel mixture tothe intake valve.

2. Description of the Prior Art

Because of operating conditions and the broad range of areas ofapplication, contemporary four-stroke Otto engines are designed for alarge rpm/load range. To realize high torque and output data, and anacceptable efficiency and exhaust-gas emission ratio in partial-loadoperation and/or in the lower rpm range, compromises in design must bemade with regard to the design of the valve-control time, the valvestroke, the valve seat geometry, the structure of the intake conduit andintake system, and the mixture formation. The primary operating range ofthe engines lies within the lower rpm/load range, i.e., at an effectivemedium pressure of 0 to approximately 5 bar and at an rpm between theidling rpm and approximately 3500 l /min. This operating range coversthe dwell period in the test cycles prescribed for type and series/modelstandard for determining exhaust gas emissions and fuel consumption upto above 90 percent.

In four-stroke Otto engines, quantity-controlled output control isregulated by the mass of working fluid used. In a camshaft-controlledload change, a throttling of the fresh intake mass is necessary in orderto be able to operate the engine in all operating ranges, that is, fromidling operation with a low fresh intake mass to full-load operationwith a fully open throttle element. In these throttle-controlledengines, an adaptation of the charge composition (residual gas, freshintake mass) and an rpm-dependent adaptation of the valve control timesto full-load operation is typically effected solely by a phase shift ofthe valve control times.

Throttle-free control of the fresh intake mass used is not possible inthe entire operating range with this phase shift. For operation athigher rpms and loads, the intake valve cross-section must be enlargedfor the charge change. This is realized in a practical manner by theconnection of one or a plurality of valves. These connectable valves canbe operated by means of a camshaft, in which case the charge quantity isthrottle-controlled. Stepless regulation and control of the chargequantity and the charge composition can be accomplished withfully-variable intake valve control times. The charge change lossesoccurring in internal combustion engines, depending on their operatingprinciples, can thus be eliminated. Furthermore, an adaptation of thecharge composition is possible in all operating ranges.

The disadvantages of throttle-controlled combustion engines occurpredominantly in the lower rpm/load range. If this operating range isused with systems for realizing fully-variable control times, the fuelconsumption behavior and exhaust gas emissions are improved throughsaving throttle losses and the adaptation of the charge composition.Systems for realizing completely-variable control times, especially whenactuation is effected by electromechanical setting units, can bedesigned especially for this lower operating range in the characteristicfield with respect to optimum efficiency.

SUMMARY OF THE INVENTION

The object of the invention is to configure a four-stroke Otto engine ofthe type characterized at the outset such that the combustion process,and thus the exhaust gas emissions and fuel consumption, are improved,so that optimum fuel consumption and optimum exhaust gas values resultboth for operation in the partial-load range and the full-load range.

According to the invention, this object is accomplished in that at leasttwo intake valves are provided, with at least one intake valve servingas the main valve and at least one intake valve serving as an additionalvalve; that the main valve is connected to a camshaft via a transmissionelement; that the transmission element has an actuatable cutoffapparatus, and that the additional valve is connected to an operatingapparatus that can be actuated and with which the valve stroke and/orthe time for the valve opening and/or the time for the valve closure canbe adjusted. With a four-stroke Otto engine configured in this manner,it is possible to perform the charge change in large characteristicfield ranges, both throttle-free with fully-variable intake valvecontrol times and with throttling with intake valve control times thatare fixed or can be phase-shifted. In an embodiment according to theinvention, the actuatable operating apparatus is designed for steplessor stepwise adjustment of the valve stroke and/or of the time of thevalve opening and/or of the time of the valve closure.

Optimum adaptation to the operating requirements in both the lowerpartial-load range and the upper partial-load range, up to full load, ispossible with the aid of a four-stroke Otto engine configured in thisway, so that optimum operating conditions can be created for the entirecharacteristic field of the engine. It is possible to perform an optimumadaptation to the conditions in the lower partial-load range with thearrangement of the additional valve, by means of whose actuatableoperating apparatus the valve stroke and/or the time for the valveopening and/or the time for the valve closure can be adjusted, such thatthe main valve is held in the closed position with the aid of theactuatable cutoff apparatus. The inflow conditions, the chargecomposition and the charge quantity can be adapted precisely to theoperating conditions in the partial-load range, both for a cold startand hot running. This also permits control of the charge quantity viathe actuation of the operating apparatus, so that throttling of the massflow of the air-fuel mixture can be omitted. The consequence ofminimizing throttle losses caused by this is a distinct improvement infuel consumption. The improvement in inflow conditions is accomplishedby an adaptation of the valve stroke of the valve controlled by theoperating apparatus to the mass flow of the air-fuel mixture required inthe partial-load range. The charge composition and the charge quantityare influenced by changes in the control times, i.e., the time for thevalve opening and/or the valve closure. An electromechanically-operatingdevice, as known from, for example, DE 30 24 109 C2, is advantageouslysuited as an operating apparatus. This device has compression springsand two electrically-operating switching magnets, via which theadditional valve can be moved into two discrete switching positionslocated opposite one another, and held in this switching position by therespectively associated switching magnet. The state of equilibrium ofthe compression springs acting on the additional valve lies betweenthese two switching positions; the state of equilibrium of thecompression springs can be relocated to the region of one of the twoswitching positions via a clamping device, preferably electromechanical.This clamping device, like the two switching magnets, can be operatedelectromechanically, so that a purposeful change in the valve strokeand/or the opening or closing time of the additional valve is possibleas a function of the operating conditions in the partial-load range bymeans of a corresponding control of the respective exciting current forthe coils of the switching magnets, on the one hand, and the magnets forthe clamping device on the other. Because of the favorable actuationpossibility, this type of electromechanical operating apparatus is to beactuated via the exciting currents in order to influence the individualfunctions.

If the engine is to be operated in the upper partial-load range up tofull load, when a predetermined load and rpm limit is exceeded, theoperating apparatus for the additional valve is held in the closedposition, and the cutoff of the main valve is released, so that thepredetermined, optimum operation takes place by means of the main valve,which preferably has positive control via a camshaft.

While it is essentially possible to charge the main valve and additionalvalve by way of a common intake conduit, in an advantageous embodimentit is provided that a separate intake conduit is provided for the mainvalve, on the one hand, and for the additional valve on the other. Thispermits the intake conduit configuration for the lower partial-loadrange, i.e., the operating range in which the main valve is held in theclosed position and the supply of air or the air-fuel mixture into thecylinder only takes place via the additional valve, to be adaptedprecisely to the inflow conditions that apply for the operating range.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail in conjunction with schematicdrawings of an embodiment. Shown are in:

FIG. 1 a vertical section through a cylinder of a four-stoke Ottoengine,

FIG. 2 a view of the underside of the cylinder head,

FIG. 3 a torque-rpm characteristic field,

FIG. 4 a charge change diagram,

FIG. 5 a block diagram of an engine control.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic vertical section through the upper part of afour-stroke Otto engine in which a piston 2 is represented in itsposition in upper dead center. The cylinder 1, with piston rings 3, iscovered by a cylinder-head seal 4 with a cylinder head 5, which isprovided with a bore 6 for receiving a spark plug.

At least one outlet valve 7 per cylinder that blocks an associatedexhaust gas conduit 8 against the cylinder interior is disposed in thecylinder head 5. The outlet valve is actuated in a typical manner, via acamshaft 9, according to the charge cadence.

On the intake side, at least two intake valves 10 and 11 are provided;in the illustrated embodiment, these valves are allocated separateintake conduits 12 and 13, so that the intake valve 10 is associatedwith the intake conduit 12 and the intake valve 11 is associated withthe intake conduit 13. For better understanding of the representation inFIG. 1, it is pointed out that the sectional representation does notextend in one plane, but, as can be seen from the representation of theintake valve 10, the valves are disposed adjacently and spatiallystaggered with respect to the plane of projection. The allocation willbe explained in detail below.

The intake valve 10 is operated by a transmission element driven by acamshaft 14. The transmission element can, for example, a drag lever 15.The drag lever 15 is connected to a cutoff apparatus 16, which can beoperated purely mechanically, electromechanically ormechanically-hydraulically in such a way that, by means of the loweringof the fulcrum 17 for the drag lever 15, the drag lever 15 no longeropens the intake valve 10, and the valve remains in the closed position.The intake valve 10 serves as the main valve and, as will be explainedin detail below in connection with FIG. 3, functions during engineoperation in the upper partial-load and rpm range. The intake valve 11is connected to an actuatable operating device 18, which is constructed,for example, electromechanically, and which opens or closes the valve 11in the charge cadence in the operating cycle. The operating apparatus 18is designed such that it can be used for stepless or stepwise adjustmentof the valve stroke and/or of the time for the valve opening and/or ofthe time for the valve closure. The intake valve 11 serves as theadditional valve, and functions during engine operation only in thelower partial-load and rpm range.

Depending on the engine type, the arrangement can include the provisionof an outlet valve 7, a camshaft-controlled intake valve 10 and anintake valve 11 controlled by means of an electromechanical operatingapparatus. The number of cam-controlled valves, however, can be varieddepending on the engine type. Hence, FIG. 2 shows a view from below thecylinder head of an arrangement in which two outlet valves 7 operated inparallel and two intake valves 10 controlled in parallel via thecamshaft 14 are provided, as is an intake valve 11 that can be actuatedby means of an operating apparatus 18.

The cutoff apparatus, which actuates the fulcrum 17 of the drag lever 15of the intake valve 10 and, simultaneously, the operating apparatus 18of the intake valve 11, can now be actuated with an actuation to bedescribed in detail below, and vice versa. With this arrangement, it ispossible, as shown schematically in FIG. 3, to operate the engine in theupper partial-load range, up to the full-load line, and at high rpms ofthe air-fuel mixture via the intake conduit 12 and the intake valve 10.

A schematic characteristic field of a four-stroke Otto engine is shownin FIG. 3. The characteristic field, i.e., the dependency of the torqueon the rpm, is defined by the full-load line 19. Depending on the valvegeometry of the intake valve 11, a lower partial-load range and an rpmlimit 20 are defined; these define an upper partial-load range 22 abovea likewise predeterminable switching region 21. The control device isconfigured such that, in the lower partial-load range 20, the main valve10 is held in the closed position by means of the cutoff apparatus 16,so that operation is effected solely by the controllable operatingapparatus 18 of the additional valve 11. The desired output optimizationin the lower partial-load range is effected by the actuation of theoperating apparatus 18. As soon as the partial-load range 20 is exiteddue to the rpms and/or the decreased torque, the operating apparatus canbe deactivated in the predetermined switching range 21 by means of thecontrol system, so that the additional valve 11 remains in the closedposition and the cutoff of the main valve 10 is released, so thatoperation is now effected in the upper partial-load range in a typicalway, via the camshaft-controlled main valve 10, in which case the supplyof air or the air-fuel mixture takes place in a conventional way, via aload- and rpm-dependent, throttle-controlled charge regulation. Theswitch from operation with the additional valve to operation with themain valve and vice versa must take place as a function of the workcycle for each cylinder, for example in the exhaust phase or thecompression phase.

In FIG. 4, an operating cycle for a four-stroke Otto engine isillustrated in a cylinder pressure diagram for operation in the lowerpartial-load range. In the expansion phase, the pressure drops until,shortly before lower dead center UT is reached, it reaches a range 23,in which the outlet valve opens. The indicated region 23 shows theoption of relocating the opening time, via a corresponding camshaftadjustment, to a range prior to reaching lower dead center UT by thepiston. The exhaust phase then follows until the piston has againreached upper dead center OT. In camshaft-controlled outlet valves, theoption exists of changing the closure time of the outlet valve 7 in therange characterized by the field 24, corresponding to the desiredoperating conditions, for example in order to influence the test gascomponent in the camshaft-controlled operating range.

Because the additional valve 11 is operated by means of the operatingapparatus 18, independently of the camshaft control, in this operatingstate, the opening time 25 can now be relocated in an arbitrary andstepless manner with respect to the position of the piston at upper deadcenter OT in order to optimize the inflow conditions. For example, toimprove the cold start and hot running behavior, it is possible torelocate the opening time 25 to a later time after upper dead center OT,so that, when the additional valve 11 is closed and the outlet valve isclosed during the downward movement of the piston, a lower pressure isestablished in the cylinder, which effects a higher-speed inflow whenthe additional valve 11 is opened later. The increased inflow speedscause the turbulence of the cylinder charge necessary for athermodynamically favorable, rapid combustion. By means of anappropriate actuation of the operating apparatus 18, the time 25, i.e.,the "intake opens" time, can be relocated in a stepless manner to arange up to behind lower dead center UT before the compression phase.The associated control time 26, "intake closes," is adapted depending onthe load.

The above description of the function of a four-stroke Otto engineaccording to the invention in partial-load operation with an additionalvalve 11 shows the substantial adaptation options to the respectivelyprevailing operating conditions in this range. As stipulated by thesystem, in electromechanically-controlled valves a free passage thatcorresponds to the valve stroke must be assured.

Because the additional valve is only required for operation in thepartial-load range, that is, a correspondingly reduced intakecross-section is necessary for this operating range, the possibilityarises of reducing the maximum required valve stroke, and thus the freepassage for the valve that is assured by valve recesses cut into thepiston. This leads, in addition to the operation-stipulatedimprovements, to a more compact configuration of the combustion chamberand consequently to improved combustion with fewer unburnt hydrocarboncomponents. Moreover, as a consequence of the smaller free valvepassage, the piston thickness and thus the piston weight can besignificantly reduced, which leads to a reduction in the oscillatingmasses and a considerable reduction in friction losses of the engine.

In the upper load range 22 (see FIG. 3), the additional valve 11 is heldin the closed position by the operating apparatus 18, so that theadditional valve 11 remains closed and operation takes place exclusivelyby means of the camshaft-controlled main valve 10. The valve seatgeometry, the intake conduit, the intake system and the mixture formercan be designed for the charge throughput needed for this range, withlarger quantities of air-fuel mixture; in particular, the option existsof designing the intake conduit 12 for the main valve and the intakeconduit 13 for the additional valve to correspond to the differentquantity flows.

The position, type and number of mixture formers can be adapted to thenumber of intake conduits and the size of the intake conduits.Therefore, it is possible to provide a central mixture former, both foreach individual cylinder and for all cylinders. Furthermore, it ispossible to provide a central mixture former for operation in the lowerpartial-load range, and individual injection for operation in thecamshaft-controlled, upper partial-load range. However, because of thegood adaptation possibilities to requirements in the lower partial-loadrange, it is also possible to provide an individual injection for thisrange, and to provide a central mixture former for operation in theupper partial-load and full-load range. The individual injection cantake place into the intake pipe or directly into the combustion chamber.

FIG. 5 shows a block diagram of the actuation of the operating apparatus18 for a cylinder of a four-stroke Otto engine equipped in the wayillustrated and described in FIG. 1. Identical reference numeralsindicate identical components, so the above description can be referredto in terms of the construction and function of the engine.

For actuation of the engine, a control device 27 is provided, in which apredetermined characteristic field is stored with its individualswitching ranges, for example a lower partial-load range 20 with apredetermined rpm limit and a predetermined switching range 21 and anupper partial-load range 22, as described by way of the schematiccharacteristic field in FIG. 3. The corresponding control parameters foractuation of the ignition, the fuel supply and the control of the valvesas a function of at least the load setting and the engine rpm are storedin the computer of the control device 27.

The rpm is detected from the crankshaft 33 by an appropriate sensor 34and fed to the control device 27 as a control signal. Furthermore, theload setting, that is, the position of the gas pedal, is entered intothe control device 27 as an appropriate setting signal 35 via anappropriate transmitter, not shown in detail here. In addition to thesebasic data, the cooling water temperature (signal 36) tapped by thesensor and the external temperature (signal 37) and the ambient pressure(signal 38) can be fed to the control device as further controlparameters in order to be able to optimally generate the actualoperating conditions in the signal processing to generate thecorresponding setting signals as a function of the respective positionin the operating characteristic field.

If the engine operates in the lower partial-load and rpm rangepredetermined by the characteristic field 20 (FIG. 3), the cutoffapparatus 16 for the cam-controlled intake valve 10 is actuated by meansof an output signal 28, so that the intake valve 10 is held in theclosed position. At the same time, the fuel supply to the intake valve10 is cut off by means of the control signal 28.1, the fuel supply beingindicated by an injection nozzle of a corresponding injection system forthe upper partial-load and rpm range. At the same time, the operatingapparatus 18 is actuated by means of a corresponding control signal 29,and the additional valve 11 is opened as a function of the conditionsfor the partial-load range that are predetermined by the programmedoperating characteristic field, as described above, for example, in thedescription of FIG. 4. The fuel supply for the lower partial-load andrpm operation is controlled by means of an appropriate control signal29.1, as indicated schematically by an injection valve 32 associatedwith the additional valve 11.

We claim:
 1. A four-stroke Otto engine comprising:a cylinder having aninterior; at least one intake conduit disposed to be in flowcommunication with the interior of the cylinder for supplying at leastone of air and an air-fuel mixture thereto; at least two intake valvesbeing disposed to open and close the at least one intake conduit, eachof the intake valves having an open position and a closed position, theintake valves further including:at least one main intake valve; and atleast one additional intake valve; at least one outlet conduit disposedto be in flow communication with the interior of the cylinder forallowing exhaust gases to be exhausted therefrom; at least one outletvalve disposed to open and close the at least one outlet conduit; atleast one outlet control device operatively connected to the outletvalve for positively controlling an actuation thereof for opening andclosing the outlet conduit; main intake valve actuation meansoperatively connected to the main intake valve and including:a camshaftoperatively connected to the main intake valve for moving the mainintake valve into one of its open position and its closed position; anda transmission element connected between the camshaft and the mainintake valve for transmitting an actuation of the camshaft to the mainintake valve for moving the main intake valve into one of its openposition and its closed position, the transmission element including acutoff apparatus actuatable independently of the camshaft andoperatively connected thereto for cutting off a transmission of theactuation of the camshaft to the main intake valve for keeping the mainintake valve in its closed position in a lower partial load and rpmrange of the engine; an operating apparatus connected to the additionalintake valve for actuating the additional intake valve independently ofthe main intake valve actuation means for moving the additional intakevalve into its open position in the lower partial load and rpm range ofthe engine and into its closed position in an upper partial load and rpmrange of the engine, the operating apparatus further being adapted toadjust at least one of a valve stroke of the additional intake valve, avalve opening time of the additional intake valve and a valve closingtime of the additional intake valve as a function of engine load; anintake control device operatively connected to the intake valves andincluding:a cutoff control means connected to the cutoff apparatus ofthe transmission element for effecting an actuation the cutoff apparatusfor keeping the main intake valve in its closed position in the lowerpartial load and rpm of the engine; and an operating apparatus controlmeans connected to the operating apparatus for moving the additionalintake valve into its open position in the lower partial load and rpm ofthe engine and into its closed position in the upper partial load andrpm of the engine and for adjusting at least one of the valve stroke ofthe additional intake valve, the valve opening time of the additionalintake valve and the valve closing time of the additional intake valveas a function of load conditions of the engine.
 2. The four-stroke Ottoengine according to claim 1, wherein the operating apparatus isconfigured for stepless adjustment of at least one of the valve strokeof the additional intake valve, the valve opening time of the additionalintake valve and the valve closing time of the additional intake valve.3. The four-stroke Otto engine according to claim 1, wherein the atleast one intake conduit includes at least two intake conduits, the mainintake valve being disposed to open and close one of the at least twointake conduits, and the additional intake valve being disposed to openand close another one of the at least two intake conduits.
 4. Thefour-stroke Otto engine according to claim 2, wherein the at least oneintake conduit includes at least two intake conduits, the main intakevalve being disposed to open and close one of the at least two intakeconduits, and the additional intake valve being disposed to open andclose another one of the at least two intake conduits.
 5. Thefour-stroke Otto engine according to claim 1, wherein the cutoffapparatus is one of mechanically, electromechanically and hydraulicallyoperated.
 6. The four-stroke Otto engine according to claim 1, whereinthe operating apparatus is electromechanically operated.
 7. Thefour-stroke Otto engine according to claim 1, wherein, in the upperpartial load and rpm range of the engine, the transmission element isadapted to actuate the main intake valve into its open position.
 8. Amethod of operating a four-stroke Otto engine comprising:a cylinderhaving an interior; at least one intake conduit disposed to be in flowcommunication with the interior of the cylinder for supplying at leastone of air and an air-fuel mixture thereto; at least two intake valvesbeing disposed to open and close the at least one intake conduit, eachof the intake valves having an open position and a closed position, theintake valves further including:at least one main intake valve; and atleast one additional intake valve; at least one outlet conduit disposedto be in flow communication with the interior of the cylinder forallowing exhaust gases to be exhausted therefrom; at least one outletvalve disposed to open and close the at least one outlet conduit; atleast one outlet control device operatively connected to the outletvalve for positively controlling an actuation thereof for opening andclosing the outlet conduit; main intake valve actuation meansoperatively connected to the main intake valve and including:a camshaftoperatively connected to the main intake valve for moving the mainintake valve into one of its open position and its closed position; anda transmission element connected between the camshaft and the mainintake valve for transmitting an actuation of the camshaft to the mainintake valve for moving the main intake valve into one of its openposition and its closed position, the transmission element including acutoff apparatus actuatable independently of the camshaft andoperatively connected thereto for cutting off a transmission of theactuation of the camshaft to the main intake valve for keeping the mainintake valve in its closed position in a lower partial load and rpmrange of the engine; an operating apparatus connected to the additionalintake valve for actuating the additional intake valve independently ofthe main intake valve actuation means for moving the additional intakevalve into its open position in the lower partial load and rpm range ofthe engine and into its closed position in an upper partial load and rpmrange of the engine, the operating apparatus further being adapted toadjust at least one of a valve stroke of the additional intake valve, avalve opening time of the additional intake valve and a valve closingtime of the additional intake valve as a function of engine load; anintake control device operatively connected to the intake valves andincluding;:a cutoff control means connected to the cutoff apparatus ofthe transmission element for effecting an actuation the cutoff apparatusfor keeping the main intake valve in its closed position in the lowerpartial load and rpm of the engine; and an operating apparatus controlmeans connected to the operating apparatus for moving the additionalintake valve into its open position in the lower partial load and rpm ofthe engine and into its closed position in the upper partial load andrpm of the engine and for adjusting at least one of the valve stroke ofthe additional intake valve, the valve opening time of the additionalintake valve and the valve closing time of the additional intake valveas a function of load conditions of the engine; the method comprisingthe steps of:moving the main intake valve into its open position andkeeping the additional intake valve in its closed position in the upperpartial load and rpm range of the engine; and keeping the main intakevalve in its closed position and moving the additional intake valve intoits open position in the lower partial load and rpm range of the engine.